Ultrasonography for Eating and Swallowing Assessment: A Narrative Review of Integrated Insights for Noninvasive Clinical Practice

Abstract

Dysphagia is a syndrome of abnormal eating function resulting from a variety of causative diseases, and is associated with malnutrition. To date, the swallowing function has been difficult to examine without the use of invasive and expensive methods, such as the videofluorographic swallowing study or fiberoptic endoscopic evaluation of swallowing. In recent years, progress has been made in the clinical application of ultrasound equipment for the evaluation of body compositions near the body surface, including the assessment of nutritional status. Ultrasound examination is a noninvasive procedure and relatively inexpensive, and the equipment required is highly portable thanks to innovations such as wireless probes and tablet monitoring devices. The process of using ultrasound to visualize the geniohyoid muscle, digastric muscle, mylohyoid muscle, hyoid bone, tongue, masseter muscle, genioglossus muscle, orbicularis oris muscle, temporalis muscle, pharynx, esophagus, and larynx, and the methods used for evaluating these structures, are provided in this study in detail. This study also aims to propose a protocol for the assessment of swallowing-related muscles that can be applied in real-world clinical practice for the diagnosis of sarcopenic dysphagia, which can occur in elderly patients with sarcopenia, and has received much attention in recent years.

Keywords: aspiration; dysphagia; swallowing function; swallowing muscle; ultrasound.

Figure 1

Imaging of the geniohyoid muscle. On the coronal section, the morphology of the geniohyoid muscle changes depending on the position of the probe. The digastric muscle and surficial mylohyoid muscle are appropriate locations to insert the probe. On the sagittal section, the probe should ideally be placed on the midline to visualize the hyoid bone and chin bone in one screen.

Figure 2

Imaging of the digastric muscle. The muscle belly is visualized by applying the probe vertical to the muscle fibers of the digastric muscle. Furthermore, the entire image is observed by sliding the probe from the chin to the top of the hyoid bone.

Figure 3

Imaging of the mylohyoid muscle. The probe is placed at the submental region and is visualized on a coronal section. When measuring muscle thickness, the probe should be placed in a position that allows the measurement of the thickness of the area where the submandibular gland wraps around the mylohyoid muscle.

Figure 4

Imaging of the tongue. On the coronal section (a), the application of the probe to the submandibular surface vertical to the Frankfurt plane allows the visualization of the central part of the tongue. Ideally, the dorsum of the tongue should be visualized on a single screen by adjusting the depth. On the sagittal section (b), the entire tongue is visualized in the deep layer by applying the probe to the midline and visualizing the geniohyoid muscle and genioglossus muscle in one screen.

Figure 5

Frankfurt horizontal plane. The Frankfurt horizontal plane is a straight line connecting the superior margin of the ear canal and the inferior margin of the orbit. As it appears almost horizontal when viewed on a natural position, the plane determined by this line on the left and right portion is called the Frankfurt plane or ear–eye plane, and is used as the standard plane to determine the position and direction of the skull.

Figure 6

Imaging of the masseter muscle. To visualize the masseter muscle, the probe can be placed vertical to the muscle fibers or horizontal to the muscle fibers. The entire area, including the bone attachment site, is visualized, and the thickest site is measured. As the purpose of the examination is to evaluate the swallowing function, the examined patient should be placed in a sitting position and looking forward or slightly downward.

Figure 7

Imaging of the genioglossus muscle. The probe is placed vertical to the Frankfurt plane. As the genioglossus muscle partially reaches the dorsum of the tongue, the coronal section, with other muscles as the orientation point, may be a suitable standard evaluation image. 1, Digastric; 2, mylohyoid; 3, geniohyoid; 4, genioglossus; 5, the body of the tongue.

Figure 8

Imaging of the orbicularis oris muscle. The orbicularis oris muscle can be visualized by placing the probe along the margin of the upper lip (a). For the depressor anguli oris muscle, the probe should be placed vertical to the muscle fibers. Since this muscle is located just underneath the surface of the skin, a linear probe should be used (b). 1, Orbicularis oris muscle; 2, alveolar ridge; 3, depressor anguli oris muscle; 4, inferior labial artery.

Figure 9

Imaging of the temporalis muscle. The probe is placed horizontally against the superior margin of the zygomatic arch and is moved gradually in a cephalic direction toward the temporal fossa. When evaluating muscle mass, the thickest site should be measured.

Figure 10

Imaging of the pharynx. To visualize the epiglottic vallecula, the probe should be placed horizontally at the level of the hyoid bone, so that the base of the tongue and the epiglottis can serve as the orientation points and the epiglottic vallecula can be identified (a). To visualize the left pyriform sinus, the probe should be placed horizontally from the left side at the level of laryngeal prominence (b). The thyroid cartilage and common carotid artery serve as the orientation points.

Figure 11

Pharynx in a dysphagic patient. A dysphagic patient showing residues in the vallecula (a) and pyriform sinus (b) on the ultrasound image.

Figure 12

Imaging of the cervical esophagus. The cervical esophagus near the lower end of the cricoid cartilage is visualized by placing the probe longitudinal to the esophagus (a). Visualizing the thyroid gland on the surface of the esophagus provides clear images with less artifacts and noise. In the horizontal section, the esophagus can be visualized deeper than the thyroid gland, on the side of the trachea (b).

Figure 13

Imaging of the larynx. When imaging on a horizontal section, the probe is placed at the level of the thyroid cartilage; the vocal fold and arytenoid cartilage can be visualized when the patient speaks (a). On the sagittal section, the vocal cords, trachea, and trachea wall can be visualized by placing the probe on the midline of the thyroid cartilage (b).